抄録
Introduction: We considered that proximal fixation is best for cementless THA, and have used custommade stems based on the morphology of the medullary space in the proximal femoral region. For smooth insertion of a stem into the femoral medullary space, the stem is designed to be as short as possible. In this study, we investigated the results of treatment using a custom-made THA stem with a length of 10cm or less, and evaluated the optimal length of the cementless stem for Japanese patients.
Subjects and methods: The subjects were 56 patients (58 hips) who had undergone treatment using an Expert system ver. 1 custom-made stem (Japan Medical Material, Osaka, Japan) and follow-up observation for more than 5 years. The patients were 15 males (15 hips) and 41 females (43 hips) with a mean age of 57 years (range 21-74 years) at the time of surgery. Their mean height was 154 cm (140-181 cm) . The mean follow-up period was 6.5 years (5-9 years) . The stem surface was sandblasted in 31 stems and hydroxyapatite (HA) -coated in 27 stems, and the mean stem length was 95 mm (83-100mm) . Clinical evaluation was performed using the JOA score, and thigh pain was examined. Radiographically, the stem stability and stress shielding were examined according to the Engh classification.
Results: The mean JOA score improved from 43 points (17-74 points) before surgery to 87 points (68-97 points) after surgery. Thigh pain was observed in 3 of the 31 hips in the sandblasted group (9.7%) and in 4 of the 27 hips in the HA-coated group (14.8%), but it disappeared in all of the hips within 6 months after surgery. With regard to stem stability, 1 of the 31 hips in the sandblasted group was radiographically determined to be in a stable fibrous fixation, while in the remaining hips, it was bone ingrown. Stress shielding of grade 3 or higher was observed in 8 of the 58 hips (14%) .
Discussion: We evaluated patients who had undergone treatment using a custom-made stem with a length of 10 cm or less, in whom good outcomes were clinically and radiographically observed. Stems manufactured mainly in Europe and America are generally too long for Japanese patients, and short stems as evaluated in this study are considered better for proximal fixation. Furthermore, short stems are useful from the viewpoint of bone conservation.
